The present invention relates, in general, to optical logic systems, and more particularly to interconnected semiconductor ring lasers responsive to selected optical inputs to produce corresponding optical logic outputs.
The general concept of utilizing active light elements for achieving logic is generally based upon the discrimination between the presence and absence of laser oscillation. Laser flip-flop devices having two stable states which make them suitable for use in information storage have been known for many years, but for such devices to serve as logic elements, a number of similar active elements must be combined. This creates difficulties which the prior art has tried to solve in a variety of ways. For example, U.S. Pat. No. 3,599,019 approaches the problem by providing a laser device having three or more stable states. A laser oscillator and an element having a non-linear absorption coefficient are combined, in accordance with this patent, so as to make it possible to select the presence or absence of light oscillation as well as the light propagation direction. Suitable detectors are provided to measure the light produced by the laser device.
Another approach is illustrated in U.S. Pat. No. 3,585,413 which provides an optical logic circuit which includes a plurality of bistable laser flip-flops divided into groups which are connected in cascade. The plural groups are pumped by two-phase pumping inputs which are successively switched at overlapped periods so that the cascade arrangement carries out binary logic operations.
U.S. Pat. No. 3,984,785 discloses another optical logic device in which the direction of polarization of a laser output is used as the logic building block.
Electronic solid state logic circuits have reached a high state of development, but as these circuits approach their limits of speed and size, logic based on photons, rather than electrons, becomes increasingly attractive, for such systems are capable of operating at or near the speed of light, and are immune from the capacitive and resistive problems associated with electronic circuits. The logic elements described in the foregoing patents have attempted to take advantage of these benefits, but suffer from such problems as fan-out and switching speed, and accordingly they have not been completely satisfactory.